This invention concerns a method for the production of alkylene carbonate, especially high purity alkylene carbonate.
Alkylene carbonates are well known materials that have been produced commercially for decades. Alkylene carbonate may be manufactured by a variety of methods. One such method is described in U.S. Pat. No. 2,773,070 (1956). Some applications of alkylene carbonate demand use of very high purity products. For example, when alkylene carbonates are used as solvents for electrolyte salts in lithium batteries, the alkylene carbonate preferably contain essentially no impurities (e.g., glycol less than 20 parts per million (xe2x80x9cppmxe2x80x9d)) and very low water amounts (also less than 20 ppm). In the past, such purification was accomplished, for instance, by treatment by distillation; however, the impure streams from the distillation tower(s), which may constitute up to 50 percent of the effluent from the carbonate reactor, are typically considered useless by-products that are destroyed. The present inventors have recognized that a need exists to remedy this wasteful practice and to provide a more economical process. The present inventors have also recognized that a need exists for high purity alkylene carbonate on a commercial scale.
In addition, it is known that elemental carbon in various forms is suitable for use in contact treatment for removing impurities from a variety of fluid materials including air, and liquids such as water and organic liquids. Elemental carbon is known to exist in a variety of forms, including amorphous forms including soot, carbon black, charcoals, and lampblack. The macroscopic properties of these materials depend upon their particle size and surface area. Of these several forms, the charcoals, and particularly activated charcoal, find frequent employment in the treatment of the aforesaid substances. Activated charcoal is a porous, microcrystalline carbonaceous material having a surface area between about 500 to 1500 square meters of surface area per gram. It is presumed that the purification of various substances contacted with charcoals occurs through the mechanism of adsorption of various chemical species upon the surface of the charcoal.
Organic liquids including but not limited to alkylene carbonates and in particular propylene carbonate often contain undesirable impurities acquired either through the manufacturing process or from packaging and conveyance. It is known in the art that the use of pre-treated carbons, such as acid-washed carbon, can remove color bodies (impurities having a color that can be seen by the human eye) of many organic compounds.
On the other hand, however, alkylene carbonates having a very low ultraviolet light UV absorbance were until recently of little or no importance commercially. Recently, the alkylene carbonates having low UV absorbance may be used in applications where electrochromic or photochromic grade alkylene carbonate is needed. These optical applications require very low alkylene carbonate absorbances that are typically lower than those that can be achieved by typical distillation. The target UV absorbances are less than about 0.350 at 220 nanometers (nm), with less than about 0.310 nm being preferred, and less than about 0.930 at 215 nm, with less than about 0.910 being preferred. These values are in neat solution (not diluted). Hence, processes to produce carbonates having a UV absorbance near the detection limits of current analytical instrumentation are nonexistent. As used to herein, measurement of ultraviolet light (xe2x80x9cUVxe2x80x9d) absorbance refers to UV light having wavelengths in the 220-350 nanometer range. For instance, until recently, there was no need for electronics grade propylene carbonate.
The inventors have recognized that a need exists for processes to manufacture alkylene carbonates having very low UV absorbance. The inventors have discovered a process for treatment of alkylene carbonates with charcoals that have been treated which unexpectedly provides an alkylene carbonate that nears the current detection limits for UV absorbance.
The present invention provides a solution to one or more of the disadvantages and deficiencies described above.
In one broad respect, this invention is a process useful for the manufacture of alkylene carbonate, comprising: contacting carbon dioxide, an alkylene oxide, and a carbonation catalyst in a reaction zone to produce a crude reactor effluent; subjecting the crude reactor effluent to low temperature evaporation to form an evaporator overhead containing alkylene carbonate and an evaporator bottoms stream containing the catalyst, and recycling the evaporator bottoms stream to the reaction zone, removing any light components present in the evaporator overhead to form a second evaporator overhead and recycling the light components to the reaction zone; distilling the second evaporator overhead to form a first distillation overhead stream and a first distillation bottoms stream containing alkylene carbonate, and recycling the first distillation overhead stream to the reaction zone; distilling the first distillation bottoms stream to form a second distillation overhead stream and a second distillation bottoms stream and recycling the second distillation bottoms stream to the reaction zone; distilling the second distillation overhead stream to form a third distillation overhead stream and a third distillation bottoms stream and recycling the third distillation overhead stream to the reaction zone; distilling the third distillation bottoms stream to form a fourth distillation overhead stream containing purified alkylene carbonate and a fourth distillation bottoms stream, and recycling the fourth distillation bottoms stream to the reaction zone. Optionally, this embodiment may include contacting the purified alkylene carbonate with carbon to reduce the UV absorbance of the purified alkylene carbonate.
In another broad respect, this invention is a process useful for the manufacture of alkylene carbonate, comprising: distilling a first stream containing an alkylene carbonate in a purity of about 99 percent or more to form a first bottoms stream containing alkylene carbonate at a purity greater than the purification stream and an first overhead stream containing alkylene carbonate at a purity greater than the purification stream, and introducing the first overhead stream to an alkylene carbonate reactor; distilling the first bottoms stream to form a second overhead stream containing high purity alkylene carbonate and a second bottoms stream, and recycling the second bottoms stream to the alkylene carbonate reactor. Optionally, this embodiment may include contacting the purified alkylene carbonate with carbon to reduce the UV absorbance of the purified alkylene carbonate.
In another broad respect, this invention is process useful for the manufacture of alkylene carbonate, comprising: contacting carbon dioxide, an alkylene oxide, and a carbonation catalyst in a reactor to produce a crude reactor effluent; subjecting the crude reactor effluent to low temperature evaporation to form an evaporator overhead containing alkylene carbonate and an evaporator bottoms stream containing the catalyst, and recycling the evaporator bottoms stream to the reactor, removing any light components present in the evaporator overhead to form a second evaporator overhead and recycling the light components to the reactor; distilling the second evaporator overhead to form a first distillation overhead stream and a first distillation bottoms stream containing alkylene carbonate, and recycling the first distillation overhead stream to the reactor; distilling the first distillation bottoms stream to form a second distillation overhead stream and a second distillation bottoms stream and recycling the second distillation bottoms stream to the reactor; distilling the second distillation overhead stream in a distillation column to form a third distillation overhead stream, a high purity middle fraction having a purity of at least 99.99% and a third distillation bottoms stream, withdrawing the middle fraction from the column, and recycling the third distillation overhead stream and the third distillation bottoms stream to the reactor. Optionally, this embodiment may include contacting the purified alkylene carbonate with carbon to reduce the UV absorbance of the purified alkylene carbonate.
In yet another broad respect, this invention is a process useful for the manufacture of ethylene carbonate, comprising: contacting carbon dioxide, an ethylene oxide, and a carbonation catalyst in a reactor to produce a crude reactor effluent; subjecting the crude reactor effluent to low temperature evaporation to form an evaporator overhead containing ethylene carbonate and an evaporator bottoms stream containing the catalyst, and recycling the evaporator bottoms stream to the reactor, removing any light components present in the evaporator overhead to form a second evaporator overhead and recycling the light components to the reactor; subjecting the second evaporator overhead to a second low temperature evaporation to form a less pure fraction and a more pure fraction, and recycling the less pure fraction to the reactor; and either: (1) distilling the more pure fraction in a distillation column to form a less pure overhead fraction, a high purity middle fraction having a purity of at least 99.99% and a less pure bottoms fraction, withdrawing the middle fraction from the column, and recycling the less pure overhead fraction and the less pure bottoms fraction to the reactor, or (2) distilling the more pure fraction to form a distillation overhead stream and a distillation bottoms stream and recycling the distillation overhead stream to the reactor; distilling the distillation bottoms stream to form a second distillation overhead stream containing purified alkylene carbonate having a purity of at least 99.99% and a second distillation bottoms stream, and recycling the second distillation bottoms stream to the reactor. Optionally, this embodiment may include contacting the purified alkylene carbonate with carbon to reduce the UV absorbance of the purified alkylene carbonate.
In one broad respect, this invention is a process useful for the manufacture of alkylene carbonate, comprising: contacting carbon dioxide, an alkylene oxide, and a carbonation catalyst in a reaction zone to produce a crude reactor effluent; subjecting the crude reactor effluent to low temperature evaporation to form an evaporator overhead containing alkylene carbonate and an evaporator bottoms stream containing the catalyst, and recycling the evaporator bottoms stream to the reaction zone, removing any light components present in the evaporator overhead to form a second evaporator overhead and recycling the light components to the reaction zone; distilling the second evaporator overhead to form a first distillation overhead stream and a first distillation bottoms stream containing alkylene carbonate, and recycling the first distillation overhead stream to the reaction zone; distilling the first distillation bottoms stream to form a second distillation overhead stream and a second distillation bottoms stream and recycling the second distillation bottoms stream to the reaction zone; distilling the second distillation overhead stream to form a third distillation overhead stream and a third distillation bottoms stream and recycling the third distillation overhead stream to the reaction zone; distilling the third distillation bottoms stream to form a fourth distillation overhead stream containing purified alkylene carbonate and a fourth distillation bottoms stream, and recycling the fourth distillation bottoms stream to the reaction zone. This process may further comprise contacting the purified alkylene carbonate with carbon to reduce the UV absorbance of the purified alkylene carbonate.
In another broad respect, this invention is alkylene carbonate having a ultraviolet absorbance of less than 0.35 at 220 nanometers.
In another broad respect, this invention is a process useful for reducing the ultraviolet absorbance of an alkylene carbonate, comprising: contacting an alkylene carbonate with carbon under conditions effective to reduce the ultraviolet absorbance of the alkylene carbonate.
This process of contacting the alkylene carbonate with the carbon imparts superior UV light absorbance characteristics to the alkylene carbonate. Typically, the starting material for is colorless in the spectrum visible to the human eye. The carbon serves to remove colorless impurities that increase the UV absorbance of the starting alkylene carbon. The process employs a charcoal (carbon) that has been treated by contacting the charcoal with an inorganic acid, rinsing the charcoal with a solvent, and optionally drying the charcoal. The alkylene carbonate may be contacted with the so-treated charcoal to reduce the UV absorbance of the alkylene carbonate. The contacting may occur in a variety of ways, including contact in a packed column where the alkylene carbonate is flowed through the charcoal bed. The purified alkylene carbonate frequently a UV light absorbance at a wavelength of 220 nanometers (nm) of 1 or less, and an absorbance of 0.4 or less at 215 nm. This represents a substantial advantage over the prior art methods which, in the case of alkylene carbonates, is especially beneficial when the alkylene carbonate is to be employed as a raw material in the manufacture of products requiring ultra high purity alkylene carbonates.
This invention has a number of advantages. For example, high purity alkylene carbonate may be produced more cost-effectively as compared to existing practices. The process of this invention, furthermore, generates less waste and higher yields than existing processes. Advantageously, this process may be implemented using conventional equipment.